This invention may be embodied in heavy-duty vacuum cleaners of the type intended for workshop use, such as in wood shops, machine shops, or for industrial applications, namely, a hybrid shop vacuum/dust collector, having a higher capacity (more CFM) than a standard shop vacuum. The invention is more particularly concerned with an improvement in a heavy duty portable vacuum in which there are a two or more dust separation stages, with the large majority of the dust being separated cyclonically and deposited into a drum or barrel, and with the remaining dust that is carried in the vacuum machine air stream being filtered out in a final filter, so that the vacuum cleaner machine exhausts clean, filtered air into the ambient. A vacuum fan or blower in the unit pulls the air stream through the final filter and exhausts it as filtered air into the ambient.
Industrial vacuum cleaners and shop vacuum cleaners are often employed for picking up dust that has accumulated on the shop floor and on surfaces of equipment, or may also be connected to a dust outlet of a dust-producing tool, i.e., wood working machines, such as sanders, joiners, and the like, or machines that process metals, plastics, or other composites such as concrete or stone. In these industrial vacuum devices, there is typically a vacuum head and a drum or barrel. The vacuum head has a blower that is powered by an electric motor to induce a suction to draw a stream of air into the machine. The airstream is then directed into the barrel, where dust collects. From there, the air stream passes though a bag filter or other filter, and is exhausted to the ambient.
In most cases, the vacuum filter does not filter out fine dust, and there is always at least some of the dust that passes out and back into the ambient air. This airborne fine dust can present a health hazard, and in a wood shop environment airborne particulates constitute a serious quality issue as the airborne dust can contaminate varnish or other wood finishes.
The dust that is collected can quickly clog and blind the filter also, which limits air flow and diminishes the efficiency of the vacuum cleaner. Moreover, filling of the filter material requires that the vacuuming operation be interrupted frequently for cleaning and/or replacing of the filter.
A shop-type vacuum cleaner with a cartridge type final filter to capture fine dust particles has been proposed previously, and an example of such a shop vacuum is described in U.S. Pat. No. 5,069,696. In that case, an externally-mounted filter is located in the exhaust air stream in a housing that is disposed outside the vacuum machine drum or canister. This arrangement exhausts significantly cleaner air back into the ambient, but because the air passes directly from the main collection drum out to the filter housing, the filter accumulates dust quickly and requires frequent cleaning for effective operation.
It has been proposed previously to employ a cyclonic separator in line in a vacuum hose in advance of a shop vacuum cleaner for pre-separating particulate matter, and then with the outlet pipe of the cyclonic separator connecting to the inlet of the vacuum cleaner. This arrangement is described, for example, in U.S. Pat. No. 7,282,074. This system can result in removal of about ninety percent, or more, of the dust from the air stream ahead of the vacuum cleaner, so that the vacuum cleaner operates longer and more efficiently in most applications. However, this arrangement requires attaching the cyclone as a separate element in between the shop vacuum cleaner and the dust producing tool or dust pick-up tool.
The portable vacuum and dust collector can be used in cabinetmaking, carpentry and similar trades, in which a flammable process dust is directed to a dust storage drum and in which the air that is separated from the dust is returned to the ambient. In equipment of this type is advantageous that the dust separator vacuum cleaner incorporate a feature for suppressing or arresting flame that may come about by inadvertent ignition of the dust in the process air stream.
A conventional flame arrester, deflagration arrester, or flame trap is a piece of equipment installed in an industrial process to stop the propagation of a deflagration traveling along a pipeline by extinguishing the flame. Flame arresters are used on storage tank vents, fuel gas pipelines, storage cabinets, the exhaust system of internal combustion engines, Davy lamps and ovenproof drums. Flame arresters function by forcing a flame front through channels that are too narrow to permit the continuance of a flame. These passages can be regular, like wire mesh, or irregular, such as those in random packing or tight screening where the heat from the flame propagation is conducted to the metal screen or mesh lowering the heat output and containing the flame front.
Such deflagrations may occur in dust collection systems that use filters, (typically pleated cartridge filters) from dust extracted from dust generating tools and processes. Flammable dust in suspension when ignited can deflagrate or burn quickly, producing flame propagation that radiates out from the source of combustion. Dust collection systems that experience this type of upset can explode unless adequately protected or vented to atmosphere. This invention will eliminate or reduce flame propagation from a deflagration that is vented through a filter (e.g., pleated cartridge filter), so that the flame front is suppressed before the separated air exits to ambient air. The conventional technique employs a semi-passive system where the deflagration is diverted through a pressure panel or controlled gate to a flame-quenching or flame-squelching device (i.e., “quelching”). These can be very expensive and complex, requiring gates, dampers, and abort gates that have to be timed electronically and must actuate in small fractions of a second. Cyclone systems are particularly difficult to adapt to the conventional technique because the flame from a deflagration must be diverted, but at the same time the outlet flow from the system must be simultaneously blocked off, requiring complex and expensive sensors and controls, and also requiring elaborate engineering control equipment.